Planetesimal Accretion in Binary Star Systems
- 1 November 2000
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 543 (1), 328-339
- https://doi.org/10.1086/317091
Abstract
Planetesimal accretion in close binary systems is a complex process for the gravitational perturbations of the companion star on the planetesimal orbits. These perturbations excite high eccentricities that can halt the accumulation process of planetesimals into planets also in those regions around the star where stable planetary orbits would eventually be possible. However, the evolution of a planetesimal swarm is also affected by collisions and gas drag. In particular, gas drag combined with the secular perturbations of the secondary star forces a strong alignment of all the planetesimal periastra. Since periastra are also coupled to eccentricities via the secular perturbations of the companion, the orbits of the planetesimals, besides all being aligned, also have very close values of eccentricity. This orbital "phasing" strongly reduces the contribution of the eccentricity to the relative velocities between planetesimals, and the impact speeds are dominated by the Keplerian shear: accretion becomes possible. This behavior is not limited to small planetesimals but also affects bodies as large as 100 km in diameter. The effects of gas drag are in fact enhanced by the presence of the constant forced component in the orbital eccentricity of the planetesimals. We describe analytically the periastron alignment by using the secular equations developed by Heppenheimer, and we test the prediction of the theory with a numerical code that integrates the orbits of a swarm of planetesimals perturbed by gas drag and collisions. The gas density is assumed to decrease outward, and the collisions are modeled as inelastic. Our computations are focused on the α Centauri system, which is a good candidate for terrestrial planets as we will show. The impact velocities between planetesimals of different sizes are computed at progressively increasing distances from the primary star and are compared with estimates for the maximum velocity for accretion. According to our simulations in the α Centauri system, the formation of a planet within 2 AU of the primary star is possible because of the orbital phasing forced by gas drag.Keywords
This publication has 20 references indexed in Scilit:
- Long-Term Stability of Planets in Binary SystemsThe Astronomical Journal, 1999
- A Circumstellar Dust Disk around T Tauri N: Subarcsecond Imaging at λ = 3 MillimetersThe Astrophysical Journal, 1998
- Gas drag effects on planetesimals in the 2:1 resonance with proto-JupiterPlanetary and Space Science, 1997
- Direct Imaging of Circumstellar Disks in the Orion NebulaThe Astronomical Journal, 1996
- Collisional Evolution of Asteroid FamiliesIcarus, 1995
- Pre-Main-Sequence Binary StarsAnnual Review of Astronomy and Astrophysics, 1994
- Nebular Gas Drag and Planetary AccretionIcarus, 1993
- Modelling the outcomes of high-velocity impacts between small solar system bodiesCelestial Mechanics and Dynamical Astronomy, 1993
- Orbital resonance in a dissipative mediumIcarus, 1978
- The Gas Drag Effect on the Elliptic Motion of a Solid Body in the Primordial Solar NebulaProgress of Theoretical Physics, 1976